willis



Aug. 28, 1928. 1,682,101

B. D. w|| |s TELEPHONE TRUNK CIRCUITS Filed May 19. 1922 @l 2 Sheets-Sheet 1 l 4 '4- fing- Aug. 28, 1928. 1,682,101

B.ID.VVILLJS TELEPHONE TRUNK CIRCUITS File M y 19. 1922 2 Shuts-Shoot 2 if! u P at ented Au 28, 1928.

UNITED STAT-ES PA E OFFICE;

BERNARD D. WILLIS, or OAK PARK, rumors, Assrsivon;

BY IVIIEH'SITIE ASSIGNMENTS,

T0 AUTOMATIC ELECTRIC INC, OF'CHICAGO, ILLINOIS; A CORPORATION OFDEILA- WARE.

Application fiied'ma 19 over the trunk extending to the switching equipment in theautomatic ofiice, and. due to this false impulse the operatorfails to obtain the desired connection. A particular object of the invention is to eliminate the possibility of a falseimpulse of current being sent over a trunk circuit of this character under the-conditions above set forth.

Another object of the invention is to provide means for signalling the operator in the manual exchange if she fails to restore the dial key in her cord circuitto normal after having set up the call and before the called subscriber answers. I

A further object of theinvent-ion is, to provide animproved repeater circuit Wherebythe setting of the operatorscalling device prepares the impulsingcircuit instead of the first impulse sent by the calling'device as has been the case-heretofore. There are other objects of the invention which, together with those specifically pointed out above, will be described hereinafter reference being' had to the accompanying drawings forming part of this specification.

Referring now tothe drawings, Figs. 1 and 2 show by means of the usual circuit diagrams sufiicient of the apparatus in the system .to enable the invention to be readily explained and understood. i i

R ferring now more particularly to- Fig. 1, the equipment shown islin the manual exchange. The reference'character A indicates a manual'substation of the ordinary typev having the usual line equipment at the exchange. -One of the operators cord circuits is indicated by the reference character O; At' thejright of the sheet; inclicated by reference character D, there is shown a trunk line comprising conductors 70 and 71 whichextends to thedistant auto matic exchange; Thistrunl; line isfp'ro-= TELEPHONE TRUNK cmovirs 192 2 Serial No. 5 2,191.

videdatfthe manual exchange with a group" of relays which serve tolrepeat impulses over thetrunl: line in'a manner similar to ordinary two'wirerepeater. The trunk'line terminates at the manual exchange in'the 'jackJQ' a i I' .In F 2, the trunk line mentioned terminates infthe :incoming' first selector Theselector E is a vertical and rotaryswitch of the' usual Strowger type and is operated according: to the two Wiresystem of control.

Accessible-to the'first selector E is a plurahty of connectors such as the one indi-- catedin the drawings and designated by the reference character HL' Only a portion of the circuits. of: the connector Hhave been shown. However, it will be understood that this connector is. of the ordinary .Strowger vertical and rotary two wiretype. v I r 'The connector H has access to subscribers lines in the automatic exchange One of these vbeing that ioffthesubstation A ter Urinating;v in the'bank contacts 213+215, inclusive. The substation A is of the usual automatic type being provided, with the call-j switches. H r i Theline'of thesubstation-A' terminates, at the, exchange in the individual. line or trunk selecting switch C The line switch C is of the, usual rotary type whose Wipers in rdeviceS for controlling the'centralofiice have no normal position always remaining in engagement, when idle, with the bank congacts associated with the trunk line last use v Although only;alfirst selctor shown in the drawingslit will be understood that the size 'o f,-thej exchange is im '-l mater al, and maybe increased inthe usual manner byjinsertinglselectors between the first selectorfE "and,the connector'H. 7

At D,' I1,ig. -l, is shown a ino dification of thetrnnk circuit D which has ahighergrade of transmissionthan the trunk circuit D. e Havinn'described the apparatus shown in the drawings, its cletaiIed cirGuitoperation when the subscriber at substation'A inthe manualexchange desires [to call a subscriber IUU at, substation A 'in'the "automatic exchange I will nowbe explained, a V a I c W he r ceiv ri mcved .a su sta tic-111A, a circuitis, close 15 which attracts its armature 18 and lights 5 t-h line 3 1 eration signals the operator at whose position the answerlngjack J appears, and she will III I closes the circuit of the plug P respond to the call by inserting the answering plug of an idle cord circuit, the cord circuit O for example, in answering jack J. When the plug is inserted in the jack, the cut off relay 16 is energized, the circuit of the line relay is broken and the line lampL is extinguished. At the same time a circuit is completed over the sleeve of the cord for answering supervisory lamp L, but since i 7' is off the hook at substation A,

the receiver the supervisory relay will at once operate to shunt out the lampL to prevent it lighting at the present time. The operator may now throw her key K into listening position in order to answer the calling subscriber and ascertain'what number is desired. 7 Having found that the desired party is the subscriber at substation A in the distant automatic exchange; the operator will test the jacks associated with the trunk lines extending to such exchange with the tip of the calling inthe usual manner, and will insert the plug into the first idle jack. Assuming thatithe trunk line shown in the drawings is the first idle trunk line, the calling plug P will be inserted into thejack J. A circuit is thereby established for the sleeve relay in series with the supervisory lamp L Upon energizing, relay 55 at armature 64: polarizing winding of the electro-polarized relay 51, at armature 63 closes a point in the operating circuit extending to the distant automatic exchange, and at armature closes a point in a chain circuit which'will bedescribed subsequently. Another result of theinsertion of the calling plug P into the jack J is that a circuit is completed-for the relay 54; extending from ground through the upper right hand winding of the repeating coil of the cord circuit, by way of springs V plug P, tip of jack J, through the winding of relay 54 and thence to battery by way of the normally closed springs controlledby armature 56. Relay 5a is energized over this circuit and operates to place a bridge across the trunk conductors and 71. This bridgemay be traced from trunk conductor 70 by way of armature 62 and its'rfront contact; armature 60' and its back contact, through the lower winding of the electro-polarized relay 51, through the winding of relay 53, to trunk conductor 71. Closure of the above traced bridge causes the energization of the line relay 150 of the incoming first selectorE in the automatic exchange. Relay 150,upon energizing, at its armature 155 closes a circuit for the slow acting relay 151. Upon operating, the latter relay at armature 156, opens a point in the circuit of the release magnet 158 ,at the front contact of this armature prepares the 36 on key K, tipof by establishing a locking circuit for itself exelusive of the contact 62 on the line relay. This short circuiting of spring 62 and its working contact by the energization of relay 53 prevents a false interruption being produced in the circuit of the line relay 150 of the selector E in case the circuit of the line relay 54t'should happen to be momentarily opened when the calling plug is in-. se'rted into, the jack J. This occurs some times at theinstant of plugging in due to imperfect contact between the plug and jack or to unskillful manipulation by the operator. It should be mentioned at'this time that the electro-polarized relay 51 in the. repeater D is not operated at this time as the effect at the'upper polarizing winding neutralizes the effect of the lower winding.

The foregoing operations have all taken placefautomatically inresponse to the insertion oi": the plug into the jack J. The operator will now throw the calling device key K inorder to connect the calling device Sin the control circuit of the line relay 54: of the repeater D, and will then proceed to call the digits in the number of the substation A; When the key K is thrown,'it will be seen that the springs of the calling device S are substituted for the upper right hand winding of the-repeating coil in the cord circuit 0 in the circuit otthe line relay 5a. Upon the forward movement of the calling device for the first digit of the desired number, the spring 37 on the calling device S is operated and engages its working contact. By this operation a circuit is completed extending from ground by way of the working contact of spring 37 and the said spring, spring 38 of key. K and its working contact, 'ring of plug 1?, ring of jack J, back contact and armature 57, and through the windingot the relay 52 to battery. Upon energizing, relay 52 at its arma ture (it) places a direct bridge across the trunk'conductors 70 and 71 exclusive of the windings oi relays 51 and 53; The relay 53, of course, retracts its armature, 61 thereby opening its own locking circuit. hen the calling device dial is released, in its restoration to normal, a series of interruptions is produced in the circuit" of the line relay 54: of the repeater D. By. the deenergizations'of this relay this impulse series is repeated to the line relay 150 of an incoming first selector E in the automatic exchange.

' The series of interruptions produced in the circuit of line relay 150 of the selector E causes'this relay to be deenergized a come ill) lllf) lit) llfi

Jim

itself and at its armature 162-prepares a circuit for the rotary magnet 163. Shortly after the termination of the 3 vertical movement of the switchathe slow acting relay 152 deenergizes'therebycompleting the circuit'of the rotarymagnet163. The rotary magnet-l63 operates toi-rotate the switch shaft thereby bringing the switch wipers into engagement with the first set of bank contacts on the level to whichthey were raised by the'verticalmagnet, and at armature164-o ensrthe locking circuit of the stepping re ay 153. 1 Upon retracting it's armature, :relay 153 open-s the'circuit of the rotary magnet 163 I which likewise deenergizes. The operation of theselector E now depends upon whether itswipers 170-172, inclusive, are associated with an idletrunk line or not; Assuming the associated trunk line-is busy, there will be aground potential uponthe test contact engaged by' the test wiper171 andathe -stepping relay l53 will beenergized to closea locking circuit for itself and to complete the circuit of the rotary magnet. Magnet 163 causes the switch wipers to be rotated into engagement with thefnext set of bank contacts in the selected level and opens-the circuit of the stepping relay153, which deenergizes, opening the circuit of the rotary magnet, which deenergizes also. The f alternate operation of the stepping magnet 153 and the rotary magnet 163 continue until the switchwipers are brought'into engagement with a set'of bank contacts associated with an idle trunk line. It will be assumed that the trunk line shown in the drawings terminating in the bank contacts 17317 5, inclusive, is the first idle trunk line. Immediately upon the wipers ofthe switch being rotated into en gagement with this setof bankcontacts the rotary movement of the switch ceases and the switching relay 154,:which has been short circuited during the'operation of the switch, is energized in series "with the stepping relay 153. Relay 154, upon operating, at its armature 167 grounds thetest contact 174 in order to busy the seized trunk line, at armature 168 opensthe circuit of the slow actingrelay 151, at armatures 166 and 169 disconnects the windings of the line relay 150from'the trunk conductors and 71,"and at the frontfcontacts of these arma; tures extends the said conductors byway of wipers 170 and 172, bank contacts 173 and 175, to the upper and lower windings oflinerelay-201 of the connector H."

Returning now to the operation of' the apparatus 'in the manual exchange, when. the calling device dial reaches its normal position, the circuit of the relay 52 is opened, andthis-relay deenergizesto replace the windings iofthe relaysz51 and 58 in the bridge across conductors 70 and 71. The relay 53 again energizes to short circuit the impulse: springs62 and to establish a lockingcircu'it for itself. 7 i

When the calling device S the next digit'of the desired number, the

relay 52 operates as before described to openand a series of the circuit of the relay 53, interruptionsis produced inthe circuit'of the line relay 54 of the repeater D. By the deenergizations of the line re1ay,54 this impulse series is repeated to the line relay 201 of'the connector H in the automatic exchange. The deenergizations'of the line re lay 201 in response to these interruptions control thevertical magnet of'the switchin stepping the switch shaft carrying the wipers 210-212, inclusive, step by step until the said wipers are brought opposite the level of bank cont-acts in which is. located the, contact set associated with the line-of the substation A.

In the manual exchange, when the finger hole dial returns to normal, the relay'52 deenergizes' to againreplace the relay 58in bridge of the trunk conductors 70 and 71, and this latter relay perates as before to re-establish its locking circuit. 7

The 'operatorgmay now operate her call-, ing device S in accordance with the next and final digit" ofthe desired number. By thisoperation the relays 52 and 54 in the repeater D cause the series :of'interruption to be produced in the circuit of the line relay 201 in the connector H, and the line relay 201 deenergizes a plurality oftimes to con; trol the rotary magnetis operated forof the connector in rotating the wipers of the switch into engagement with the set of bank contacts associated with the line ofthe substation A, which, as shown in the drawings, terminates in contacts 213'214, inclusive 1 Assuming that the line of the substation A is idle at the present time, the relay 220 in the line switch C will be operated to clearthe lineof its normal battery and ground connections in the usual manner and ringing current will be automatically projected out on the called line to signal subscriber at substation A: When the'receiver is removed 'at substation -A the signalling operation will proceed in the manner with the resistance its working contact, tip of plug operation ceases and by the operationof the ring cut as relay in the. connector talking current is supplied to the called substation from the winding of back bridge relay 200. Relay 200, is energized over the called line loop and, upon operating, at armatures 204 and 205 reverses the connections of the line relay 201 with regard to the trunk conductors 70 and 71 whereby the current flow through the windings of the relays 51 and 53 in bridge of these trunk conductors in the repeater D is-reversed. This reversal of current flow causes the operation of the electro-polarized relay51 in the repeater D. Upon operating, relay 51 'at armature 58f closes the circuit of the relay 50. 'The latter'relay, upon.oper-. ating, at armature-57' disconnects the relay 52 from the ring side of the trunk and at armature 56 places the line relay 54 in series 67 in bridge of the ring and tip sides-of the trunk. Assuming that the operator has already restored key K which will ordinarily be the case, this operation causes the energization of the supervisory relay 30 in the cord circuit 0. Relay 30 operates to place a shunt around the supervisory lamp which is extinguished. By the etiacement of the lamp L the operator is informed that the called subscriber has answered. Conversation between the two subscribers may nowtake place in the ordinary manner, which will be understood without further consideration.

Should the operator fail to return the key K to normal position before the called subscriber answers, the bridging of the line relay 54 across the ring and tip sides of the trunk by the energization of relay 50 causes a circuit to be completed extending from ground throughthe impulse springs of the calling device S, spring 89 of key K and P,-tip of jack J, through the winding of relay 54, iront contact and armature 56, resistance 67, ring of jackJ, ring of plug P, working con tact of spring 38 and the said spring, spring 37 of the calling device S and its resting contact, andthrough the winding ofrelay 33 to battery. The relay 33' operates over this circuit and at its armature 34 connects a lead fromthe signallingmachine T to the tertiary winding of the induction coil associated with the operators head set A tone is thus given to theoperator informing her that the calling device key K is oft normal. Upon hearing this tone, the operatorwill restore the key K to normal whereupon the already described. I V

The manner in which the connection is released will now be described. The replacement of the receiver at the calling substation A causes the lighting of the supervisory lamp L. When'the receiver is replaced at substation A, the back. bridge relay 200 in the connector H deenergizes and reverses the direction of current flow over the trunk line incoming to the selector E and through the lower winding of :electro polarized'relay 51 in bridge olisai'd trunk line at repeater D to normal. The two windings of relay 51 'now oppose each other, the said relay. retracts its-armature. and the circuit of the relay 50 is opened. The deenergizationoit' relay'50 disconnects the bridge across the ring andtip sides of the jack J whereby the circuit of the supervisory relay. 30 in the cord'circuit O is opened. Upon deenergiziug, relay 30 opens a shunt around 1 the supervisory lamp .L thereby causing this lamp to be lighted. Upon the operator receiving the disconnect signals, she will reinovethe plugs P and P from the. jack J and J. Upon'the removal ofthe plug P from the jack J the line circuit at substation A is restored to normal. oi? the plug P from the jack J the circuit of the line relay 54 as well as-the sleeve relay 55 is opened. The deenergizationvof the line relay 54 allows. the armature 62" on the line relay tofallbaclr. The deenergization of the sleeve relay 55 opens the cire cuit of the polarizing winding otthe re-.

lay 51 at armature 64 and at armature 63 opens the bridge across the conductors and 71 including the windings of relays 51 and The removal of the bridge across conductors 70 and 71causes the circuit of the line relay 201 of the connector H to be opened. In the connector H, relay 201, upon deenergizing, opens the circuit of the slow acting relay 202. Upon retracting its arma ture, relay 202 closes the circuit of the release magnet of the connector H at armature207 and at armature 203 removes ground from the release trunk conductor therebyopening the holding circuit of the selector E. The release magnet of the connector H operates to restore this switch to'itsnormal position and the release magnet 158 of the selector Eoperatesto-release the selector-E in the usual manner. In the above manner all the apparatus involved in the connection is restored to its normal position. r

Having described the operation of the repeater I), the operatioirof therepeater D Fig.1, which is a modification of the repeater D-will now be briefly described. In order to dothisit will be assumed that'in the previous connection theoperator uses a By the removal trunk circuit such as the one terminating at coming switch in the automatic exchange, and at armature 116 prepares a certain chain circuit Whichwill be fully described hereinafter. Another result of the insertion of the plug P. into the jack J is that a circuit is completed for the line relay 104 in series with the upper right hand winding of the repeating coil of the cord circuitO. Relay 104, upon operating at its. armature 113' closes a bridge across the trunk conductors 120. and 121 through the lower winding: of the electro-polarized relay 101 and through the winding of the relay .103. .The electropolarizedrelay 101 does not operate atthis time, as'the current flow in its lower winding is opposite to the current flow in its upper Winding. Relay 103, upon energizing, short circuits the impulse springs 113 on the line relay 104 thereby establishing a locking circuit for itself exclusive of these springs. This short circuit prevents false preliminary interruptions being produced in the bridge across the trunk conductors 120 and 121 in a manner similar to that before described.

When the calling device is operated in accordance with the first digit of .the desired number, the forward movement of a dial closes the circuit of the relay 102. Relay 102 operates in a manner similar to relay 52 to place a direct bridge across the trunk conductors 120 and 121. The deenergizations of the line relay 104 inresponse to the opera tion of the calling device causes the interruptions to be repeated in the line relay in the incoming first selector in the automatic exchange. The first selector in the automatic exchange operates in the usual manner, being raised to the proper level of bank contacts in response to'the digit dialled and then rotated until its wipers are brought into enagement with the bank contacts of a trunk ine extending to an idle connector switch. When an idle trunk line is found, the-eonnection is extended to the line relay of this connector switch which operates to close the circuit of its slow acting release relay. The latter relay prepares the operating'circuits of the connector and establishes a holding circuit for the operated first selector in the usual manner. Returningnow to the operation of the repeater D, upon the calling device S restoring to normal, the relay 102 is deenergized to replace the winding of relays 101 and 103 in the bridge across conductors 120 and 121.

In response to-the two succeeding-operations of the calling devices S the line relay of the repeater Doperates to repeat the im* pulse-series to the line relay of the connector inthe automatic exchange. The line relay of this connector causes the switch to establishconnection with the desired line inthe usual manner When the called subscriber answers, the back bridge relay in the connector energizes operator removing the plugs Pand P to reverse direction of current flowiz through the bridge including the: lowerwinding: of

the ele'ctro-polarized relay. 101: in. themepeater D. Relay: 101,. upon operating at its armature 109 closes lay 100. Upon operating, relay 100, at armature 106 closes a lockingcircuitefor the line. relay 104 at, the same. timedisconnecting it from the tip side'of the jackil atiarmature 107 disconnects the :relay 102 from the-ring side of the jack J and ata-rmature 108 .re.-' moves the short circuit from the upper Winding" of the sleeve relay 105. By the removal of this short circuit the currentflow is.reduced and the .lamp, L is extinguished, though the relay remains energized as before. By the elfacement of the lamp L the operator is informed that the called subscriber has answered; Conversation now-takes'place between the calling andcalled subscriber in the usual manner. When the conversation is terminated, the connection is released by the from the jacks J and J respectively. I

Itwill be: seen that when the-"called subscriber answers all bridgesare removed'from thetrunk line on theleft hand side ofthe condensers and that over the sleeve conductor. Thus higher grade of transmission issec-ured by using the repeater D thanwby-usin'g the re pea-terD. p i

The chain circuitscontrolled-by the relays 55 and 105 order to eliminate unnecessary testing of a large number of. jacks during the busy hour and will now be described: The trunk lines .arearranged in groups-10f tens, with a chain circuit foreach group, so that-the operator-will receive a busy signal upon testing the first jack of a group of ten if all ten trunks of the groupare busy, and. may next proceed to test the jack associated with -the firsttrunk line ofthe succeeding group without having to'test theother nine Jacks in the first group. To -explain this ailittle more fully, the trunk circuit D is the first one in its group, and the relayz55, upon attracting itsarmature6'5,; closes one point inthe group chaincircuit'. If all the-other trunk lines of the group are busy, .armaturessuchas 128, 129, and 130 on other relays suchas'55 will the circuitaof the re-w mentioned above are provided in i supervision is secured a slightly be closed and a lead'frointhesignalling ma 1 said trunk line, a cord circuit at said operators position for connecting a calling line 'to said trunk line, a c1rcu1t for sald line relay including conductors of said trunk line, a second relay associated with said trunk line at said operators position, means effective. when said cord circuit is connected to said trunk line for energizing said second relay toclose said circuit, and a third relay included in said circuit .then operable to maintain said circuit closed independent of said second relay.

i 2. In a telephone system, an operators position, an automatic switch, a trunk line extending from said position to said switch, a line relay for said switch bridged across said trunk line, a cord circuit at said operators position for connecting a calling line to said trunk line, a circuit for said line relay including conductors of said trunk line, a

second relay associated with said trunk line at said operators position, means effective when said cord circuit is connected to. said trunk line for'energizing said second relay to close said circuit, a third relay included insaid circuit then operable to maintain said circuit closed independent. of said second relay,

a calling device in said cord circuit, and means controlled by said calling device for deenergizing said third relay.

3..In a telephonesystem, an operators position, an automatic switch, a trunk line extending a-line relay for said switch bridged across said trunk line, a cord circuit at said operators position for connecting a calling line to said/trunk line, a circuit for said line relay including conductors of said trunk 'line, a'second relay associated with .said

' 7 4-. In a telephone-system, a trunk line com prising two inductively connected sections, a lme relay energized over the first section to close abridge across the secondsection, and

a relay included'in thebridge and responsive to the initial closure thereof for closing said bridge atanother point.

5. In a telephone system, a trunk line comprising two inductively. connected sections, an automatic'switch in which the second section terminates, a line relay-energized over the first section and having contacts for closing-a control circuitlor said switch from said position to said switch,

over the second section, and a second relay included in said control circuit and responsive to the closure thereof for shunting said contacts to prevent the control circuit from being opened by. an accidental deenergization of said line relay.

6. Ina telephone system, a trunk line comprising two inductively connected sections, an automatic switch in which the second section terminates, a line relay energized over the first section and :having contacts for closing a control circuit for said switch over the second section, asecond relay included in saidcontrol circuit and responsive to the closure thereof for shunting said contacts to prevent the control circuit from being opened by an accidental deenergization of said line relay, a calling device for controlling" said line relay over the first section to produce interruptions in said control circuit for operating said switch, and a third relay responsive to the operation of 4 said callin v device to open the shunt circuit.

7.In a telephone system, a-group of jack ending trunks, circuit arrangements for placing a'test potential on the sleeve of any jack when the associated trunk is busy, a tone machine, and means including a chain 'circuit'i or connecting said machine to the sleeve of the jack of the first trunkwhen all said trunks are busy.

8. In a telephone system, a trunk line having two talking conductors, an automatic switch terminating said trunk line, a calling device,,means responsive to the actuation of saidcalling device and controlled over one of said talking conductors for placing a bridge across said trunk line, and means controlledover the other of said talkin conductors for opening and. closing said bridge for operating :said switch;

9, In a telephone. systemya trunk line comprising two inductively. coupled sections, an automatic switch terminating the second section, a calling device, means responsive to the actuation otsaid calling. device and controlled over one ofthe talking conductors of the first section for placing a bridge across the talking conductors of the second section and means controlled overthe other talking conductor of the first section for producing. interruptions in'said bridge to operate said switch.

i 10. In a telephone system, a trunk line terminating in an automatic switch, a line relay. for said switch bridged across said trunk line, a circuit for said relay including the two talking conductors of said trunk line in series, a second relay, means effective when said trunk line is seized forenergizing said second relay to close said circuit, and a third relay included in said circuit then operable to maintain said circuit closed independent of said second relay.

11., In atelephone system, a trunk line comprising two inductively coupled sections, an automatic switch termmating the second section, a line relay energized over the first section and having contacts for closing a control circuit for said switch over the second section, said circuit including the two talking conductors in series, and a second relay included in said control circuit and responsive to the closure thereof for shunting said contacts to maintain said circuit closed independent of said line relay.

12. In a telephone system, a repeater for repeating impulses over two conductors of a trunk line in series, a line relay connected across said trunk line, impulses repeating contacts in said repeater, a calling device, means for associating said calling device with said repeater, means responsive to said first means for closing a circuit for said line relay excluding said contacts, and means responsive to the actuation of said calling device for including said contacts in said circuit to control the operation of said line relay.

13. In a telephone system, a repeater for repeating impulses over two conductors of a trunk line in series, a line relay connected across said trunk line, impulse repeating contacts in said repeater, a calling device, means for associating said calling device with said repeater, meansresponsive to said first means for closing a circuit for said line relay excluding said contacts, means'responsive to the actuation of said calling device for including said contacts in said circuit to control the operation of said line relay and for again excluding said contacts when said calling device returns to normal.

14. In a telephone system, a switch, a relay having contacts for repeating impulses to said switch, a calling device for controlling said relay, operation of said calling device for includ ing said contacts in circuit with said switch;

15. In a telephone system, a switch, a relay having contacts for repeating impulses to said switch, a calling device for controlling said relay, and means responsive to a set and means responsive to a setting ting operation of said calling device for in eluding said contacts in circuit with said switch and for excluding said contacts from the circuit again when said calling device has restored to normal.

16. In a telephone system, a trunk termi nating in a switch, a control circuit for said switch including the two sides of said trunk in series, a relay having contacts for producing impulses in said circuit, said contacts being normally ineffective, a calling device for controlling said relay, and means responsive to a setting operation of said calling device for rendering said contacts effective.

17. In a telephone system, a group of jack ending trunks, circuit arrangements for placing a test potential on the sleeve of a jack when the associated trunk is busy, and means for giving a distinctive audible signal responsive to the testing of the first trunk when all the trunks of the group are busy.

In witness whereof, I hereunto subscribe my name this tenth day of May, A. D. 1922.

BERNARD D. WILLIS. 

